In general, most existing hydrogel soft contact lens materials are based on HEMA, also known as hydroxyethyl methacrylate or as ethyleneglycol monomethacrylate, with one or more optional comonomers as described in U.S. Pat. Nos. 2,976,576, 3,841,985 and 3,985,697. Other hydrogels based on N-vinylpyrrolidone copolymers and acrylamide copolymers are disclosed in U.S. Pat. Nos. 3,639,524 and 3,929,741. These prior hydrogel polymers generally suffer from several inherent problems (a) relatively weak mechanical strength, low dissolved oxygen permeability or a combination of both (b) most lenses are made by either of two procedures, one requiring costly lathing and polishing steps and the other using delicate spin casting techniques where polymerization, crosslinking, and shaping are done simultaneously.
Polyvinyl alcohol has also been proposed as contact lens material. Several reagents have been suggested to crosslink PVA for this purpose: formalin and acid catalysis, Japanese Pat. No. 72/06910; dialdehyde of PVA with PVA and acid catalysis, Japanese Patent application No. 50/115258; and glyoxal, U.S. Pat. No. 3,408,429. These PVA crosslinked materials suffer from hydrolyzable acetal or hemiacetal linkages.
Silberman and Kohn, ACS Polymer Preprints 24, 262-3, 465-6 (1983) and J. Polym. Sci. Chem. 23, 327-336 (1985) prepared 2-benzyloxyethyl-methacrylate (BzOEMA) and graft polymerized it onto PVA by anionic and free radical catalysis. Membranes for contact lens applications were prepared by dissolving the PVA-graft-BzOEMA in dimethylsulfoxide, casting it on a Teflon surface and immersing it in acetone to precipitate a film which is later swollen in water. However such graft polymerization is generally accompanied by oxidation and degradation of the PVA and by the orientation effects in the casting procedure thereby promoting anisotropy in the mechanical properties.
Grafted PVAs have also been made by procedures that do not involve the formation of a radical on a polymer backbone. For example:
In U.S. Pat. No. 4,085,168 (1978) a PVA-graft copolymer useful as a hydrogel contact lens is made by first forming a hydrophobic macromer, such as polystyrene or polymethylmethacrylate, by an anionic mechanism and capping with a polymerizable (meth)acrylate group. This macromer is then copolymerized free radically with vinyl acetate. After hydrolysis of the acetate group a comb-like structure with a PVA backbone and pendant hydrophobic chains of similar molecular weight is produced. Though clear, transparent films can be produced by this method, the actual chemistry involves several complicated steps some of which require moisture sensitive precautions.
Also in U.S. Pat. No. 4,426,492 (1984) certain carboxylated PVA derivatives, useful as disposable, hydrogel soft contact lenses, are disclosed. It is broadly disclosed that certain carboxylated PVA derivatives may be internally plasticized by esterification with a polyglycolether such as poly(ethyleneglycol). However, esterification reactions are normally difficult to be precisely reproduced, and, in addition, mixing problems may be experienced due to phase separation of two high molecular weight polymers.
PVA has been reacted with isocyanates forming urethane linkages, for example:
In U.S. Pat. No. 3,776,889 (1973) PVA has been fully reacted with allylisocyanate for use in a photoresist printing plate composition. In U.S. Pat. No. 3,928,299 (1975), isocyanatoethyl methacrylate (IEM) was reacted with certain hydroxyalkyl methacrylate containing polymers forming a urethane linkage and the polymer used in relief printing plates or circuits to form hard, insoluble coatings.
In U.S. Pat. Nos. 4,665,123 (1987) and 4,670,506 (1987) are described polyvinyl alcohol derivatives containing pendant (meth)acryloyl units bound to the polyvinyl alcohol backbone, through urethane groups, which in the case of the former patent are further reacted with a conventional vinylic monomer, and which can be crosslinked to form soft hydrogel lenses.
PVA with ether linkages have been made, for example:
In U.S. Pat. No. 4,433,179 (1984) is described a process for the preparation of poly-allyl ethers of high degree of allylation by derivatizing polyhydroxy compounds with allyl halides under phase transfer catalysis conditions. PVA of molecular weights 2,000 and 14,000 are exemplified as being derivatized with 78% and 62% of the maximum theoretical number of double bonds.
In the European patent application EP-177296-A (1986) is described a process for the production of water-soluble unsaturated polymerizable methylol acrylamide derivatives of polyols. It is exemplified to form a poly (vinyl alcohol) with 49% of the hydroxy groups of the polymer substituted with acrylamidomethyl groups. However, no suggestion of contact lenses is taught or suggested.
In U.S. Pat. No. Re. 27,401 (1972) Wichterle and Lim prepared a PVA-methacrylate i.e. a PVA that was esterified 1% with methacrylic acid anhydride, dissolved the same to make a 25% aqueous solution, and polymerized the mixture in a flat mold using potassium persulfate and sodium thiosulfate as initiator to form a hydrogel membrane. This type of hydrogel was disclosed for contact lens use. However, such lenses tend to be fragile.
Also in U.S. Pat. No. 4,347,198 (1982) it is disclosed to mix a hydrophilic component, e.g. N-vinyl pyrrolidone, a hydrophobic component, e.g. methyl methacrylate, crosslinking agent and initiator in a solvent, e.g. dimethyl sulfoxide and crosslink the whole mixture in a mold. After equilibration in water a soft hydrogel contact lens is produced. Similarly a lens is disclosed as produced by mixing a polymethylmethacrylate with pendant vinyl groups with N-vinyl pyrrolidone and polymerizing the mixture. It is also broadly disclosed to use a PVA esterified with methacrylic acid as the hydrophilic component of a contact lens mixture.
U.S. Pat. No. 4,978,713 describes polyvinyl alcohol ether derivatives containing (meth)acryloyl units, which are optionally further reacted with a conventional vinylic monomer, and which then can be crosslinked to form a soft water-swellable hydrogel contact lens having high mechanical strength, medium to high water content, superior optical clarity and high oxygen permeability.
Japanese Sho 50-144793 describes a hydrophilic polymer containing pendant polymerizable double bond groups copolymerized with a second hydrophilic monomer to give a novel hydrophilic copolymer which can be used for biomedical devices inter alia contact lenses. The emphasis in this reference is on hydrophilicity and for the need of a second hydrophilic monomer as a necessary component in the final polymers.